In fixing an optical element, such as a crystal for X-ray monochrometer, to a holder, it has hitherto been a general practice to perform this by tightening the optical element from the front surface side or back surface side of the element with a fixing screw.
FIG. 7 is a sectional view which shows a conventional method of fixing an optical element. In FIG. 7, conventionally, a crystal (an optical element) 76 is placed on a reference surface 712 provided on the inner bottom part of a crystal holder main body 71, and by use of a fixing screw 73 which is provided in a holder upper frame 711 in a piercing manner and is provided, at the lower end thereof, with a fixing plate 72 which directly depresses the crystal 76, both ends of the crystal 76 are tightened, whereby the crystal is fixed. However, this conventional technique had the following drawbacks.
(a) The tightening of the element surface by use of a fixing screw worsens the planarity of the optical element, resulting in a decrease in the performance of the optical element.
(b) The tightening of the element surface by use of a fixing screw adds strain to the optical element, with the result that the performance of the optical element decreases.
(c) The tightening with multiple fixing screws requires skills in handling in addition to the above-described decrease in performance.
(d) If the expansion and contraction of the holder and optical element occur due to temperature changes and the like, excessive stress is applied to the optical element and in the case of a brittle optical element, breakage may occur.
(e) Because the reference for the fixing position of the optical element is the back surface of the element, the mounting accuracy of the optical element decreases due to the thickness tolerance of the element and the irregular condition of the holder contact surface.
(f) It is an established method to use an organic substance spacer having elasticity in fixing by use of a fixing screw. However, in some measuring devices on which an optical element is mounted, resistance against an electromagnetic wave to be treated is not sufficient, and a decrease in performance of the optical element occurs due to the deterioration of such measuring devices. For example, because organic substances are inferior in radiation resistance, the use of an organic substance spacer has a drawback when used in X-ray monochrometer.
(g) Because the handling of an optical element requires skills, the conventional technique is inconvenient for those who are not familiar with the handling of a crystal.
In view of these problems, the present inventors have examined conventional techniques and as a result, some documents which may have relation to the problems were found. Among these documents, in “a channel-cut crystal” disclosed in the Japanese Patent Laid-Open No. 09-49899, a proposal is made to the effect that in order to keep the parallelism of two reflecting surfaces with high accuracy even in a case where a bottom surface is bonded and fixed to a fixing bed, in base portion between the two reflecting surfaces and the bottom surface there are made incisions parallel to the bottom surface. That is, in the channel-cut crystal of this invention, by making two incisions parallel to the base portion, and not to a working surface, the effect of stress and strain from the bonded portion is reduced and as a result, the parallelism of the reflecting surfaces can be kept with high accuracy (Document 1).
Similarly, as proposals to prevent the propagation of strain by use of a slit, there are proposed “a semiconductor diaphragm” in which a trench is provided in a fixed part near a chip in order to obtain stability against ambient temperature changes of a pressure detection element (Document 2) and “a combined prism fixing structure” in which in order to reduce the effect of strain and stress after bonding and fixing, only one prism is bonded and fixed and a groove is provided near the joint surface of the two prisms (Document 3).
Document 1: Japanese Patent Laid-Open No. 09-49899,
Document 2: Japanese Patent Laid-Open No. 58-39069
Document 3: Japanese Utility Model Laid-Open No. 1-81613
However, in the proposal about a channel-cut crystal shown in Patent Document 1, the fixing of the bottom surface of the crystal is predicated on the use of an adhesive and to reduce strain due to the adhesive is the purpose of this proposal. That is, on the precondition that fixing is performed by use of an adhesive, the function of the incisions is to reduce the propagation of the strain generated in the base portion of the crystal in association with the drying of an adhesive layer on the bottom surface over to the working surface as the optical element provided in the upper part of the crystal. On the other hand, what was described above as a task in the present invention is to review a fixing method by use of a fixing screw, which produces stress and strain which are also large as with an adhesive, in the mounting of an optical element in the form of a single plate to the holder. Therefore, in optical elements having universal shapes such as an optical element in the form of a single plate, the technique of Document 1 cannot provide a solution to any of the above-described problems in the fixing of these optical elements of universal shapes to a holder by use of a fixing screw.
Also, the proposals of Patent Documents 2 and 3 which disclose strain and stress absorbing means related to elements having special shapes, such as a semiconductor diaphragm and a complex prism, cannot provide solutions to any of the above-described problems in the fixing of these elements having special shapes to a holder by use of a fixing screw in optical elements having universal shapes such as an optical element in the form of a single plate, as well as the above-described “a channel-cut crystal”.
Furthermore, in the fixing of an optical element, it is important to prevent not only strain, but also the generation of noise due to the occurrence of surface waves and abnormal transmitted waves.
The task of the present invention is to provide a method of fixing an optical element which can improve the mounting accuracy by preventing a performance decrease, such as the generation of strain in an optical element such as a crystal by solving the above-described defects in the conventional techniques and by making tightening with a fixing screw unnecessary. In other words, the task of the invention is to provide an optical element fixing structure, an optical element fixing body, an optical element and an optical element holder which makes this method possible.
Another task of the present invention is to provide an optical element fixing structure, an optical element fixing body, an optical element and an optical element holder which can solve each of the above-described problems in fixing optical elements of universal shapes, such as an optical element in the shape of a single plate to a holder by use of a fixing screw (the worsening of planarity, a decrease in element performance, a danger of breakage and a decrease in mounting accuracy due to the generation of strain, the use of an organic substance spacer, and required skills in handling).
A further task of the present invention is to provide an optical element fixing structure, an optical element fixing body, an optical element and an optical element holder which can improve the performance of an optical element by cutting noises, such as surface waves and abnormal transmitted waves, in the fixing of the optical element.